Beijing: A clash at a police station that left at least four people dead in western China`s restive Xinjiang region was "a terrorist attack," a government official said on Tuesday, but an exile Uighur group accused police of firing on peaceful protesters.

Police in the desert city of Hotan "gunned down" several rioters who attacked a police station, Xinhua said on Tuesday, the worst violence Xinjiang has experienced in about a year.

But a Germany-based exile group, World Uyghur Congress, disputed the official account. It said 20 Uighurs were killed -- 14 were beaten to death and 6 shot dead -- and 70 arrested when police opened fire on a peaceful protest, leading to fighting between the two sides.

The two accounts could not be independently resolved on Tuesday.

Beijing, wary of instability and the threat to the Communist Party`s grip on power, often blames what it calls violent separatist groups in Xinjiang for attacks on police or other government targets, saying they work with al Qaeda or Central Asian militants to bring about an independent state called East Turkestan.

"It is certain that it was a terrorist attack," Hou Hanmin, chief of the regional information office, told Reuters by telephone. "But as for which organization is behind this, we are still investigating. The number of people killed and casualties will be announced soon."

Many Uighurs -- a Muslim, Turkic-speaking people native to the region -- chafe under rule from Beijing and restrictions on their language, culture and religion. They make up less than half of Xinjiang`s population after decades of immigration by the majority Han from other parts of China.

The Global Times, a popular tabloid owned by the Chinese Communist Party`s mouthpiece, the People`s Daily, quoted Hou as saying that the rioters "carried explosive devices and grenades."

"They first broke into the offices of the local administration of industry and commerce and the taxation bureau that are close to the police station," the report cited Hou as saying. "They injured two persons there.

"When they realized the targets were wrong, they started to attack the police station from the ground floor to the second floor where they showed a flag with separatist messages," Hou was quoted as saying.

The attackers set the police station on fire before killing hostages during a stand-off with armed police, she was quoted as saying.

State television said the latest incident took place when a mob attacked a police station, taking hostages and setting it on fire.

Two hostages, a paramilitary policeman and a guard died in the violence, as well as several of the attackers, it reported. Six hostages were freed.

The Global Times said the national counter-terrorism office had dispatched a team to Xinjiang.

Calls to the governments of Xinjiang and Hotan and the ministry of public security went unanswered.

SYSTEMATIC REPRESSION

Dilxat Raxit of the World Uyghur Congress said he believed the death toll and the number of injured were likely to escalate.

"All forms of protests by Uighurs are met with violent crackdowns. The clash escalated only after the crackdown and the Chinese government later refered to it as act of `terrorism`," he said. "The Chinese government consistently uses the term `terrorism` to quieten down the demands of the Uighurs."

Hotan, also known as Khotan, is a Uighur-majority town of some 300,000 people that stretches along the ancient Silk Route and lies on the edge of Xinjiang`s forbidding desert.

In March 2008, hundreds marched through the weekly bazaar in a protest the city government blamed on ethnic separatists.

Chinese censors blocked searches on Sina Weibo, China`s Twitter-like microblogging services, on the attack. Search results for the Chinese renderings of "Xinjiang unrest" and "Hotan" showed a page that said, "according to relevant laws, regulations and policies, search results are not displayed".

In July 2009, Xinjiang`s capital Urumqi was rocked by violence between majority Han Chinese and minority Uighurs that killed nearly 200 people.

Since then, China has executed nine people it blamed for instigating the riots, detained and prosecuted hundreds and ramped up spending on security, according to state media and overseas rights groups.

China has earmarked billions of dollars for the relatively poorer southern part of Xinjiang, where Hotan is located, to try to soothe income disparities that have contributed to ethnic violence.